1. Field of the Invention
The present invention relates to golf balls. More particularly, the present invention relates to multi-piece golf balls having a core, a surrounding layer, a mid layer and a cover.
2. Description of the Related Art
Top concern to golf players for golf balls is their flight performances. The golf players particularly place great importance on flight distance attained upon shots with a driver. Use of a golf ball which can attain a great flight distance upon shots with a driver enables the golf player to hit the second shot from a point near the green. The flight distance attained upon shots with a driver correlates with the spin rate. Golf balls accompanied by a small spin rate are excellent in flight performances. The flight performances further correlate with resilience performances of the golf ball.
The golf players place great importance also on spin performances of the golf balls. Great back spin rate results in small run. By using a golf ball accompanied by a great back spin rate, golf players can allow the golf ball to stop at a target point. Great side spin rate results in easily curved trajectory of the golf ball. Golf players can achieve an intentionally curved trajectory by using the golf ball accompanied by a great side spin rate. The golf balls that are excellent in spin performances are excellent in control performances. High-level golf players particularly place great importance on control performances upon shots with a short iron.
Iron clubs have several grooves on the face. These grooves suppress slipping of the golf ball on the face. Shots with suppressed slipping achieve a great spin rate. R&A rules for iron club are going to be changed on Jan. 1, 2010. According to new rules, shapes of the grooves are regulated. Spin is less likely to be permitted with iron clubs that conform to new rules. Golf balls which are sufficiently spun even when hit with an iron club that conforms to the new rules have been demanded.
When a golf ball placed on rough is hit, turfgrass is interposed between the golf ball and the face. This turfgrass promotes slipping of the golf ball on the face. A shot accompanied by excessive slipping results in reduced spin rate. Golf balls which can be accompanied by sufficient spin even when hit on rough have been demanded.
Golf balls having a cover produced using a polyurethane have been commercially available. A polyurethane is soft, in general. This golf ball is likely to be spun. This cover is responsible for control performances. On the other hand, when this golf ball is hit with a driver, the cover may lead to excessive spin. This cover interferes the flight performance.
In order to achieve well-balanced flight performances and control performances, a variety of proposals have been made. Japanese Unexamined Patent Application Publication No. H8-336617 discloses a golf ball having a core with a two-layer structure, and a cover with a two-layer structure. US 2002/119840 (Japanese Unexamined Patent Application Publication No. 2002-191719) discloses a golf ball having a core and a cover with a three-layer structure. US 2005/075196 (Japanese Unexamined Patent Application Publication No. 2004-180822) discloses a golf ball having a core, an inner mid layer, an external mid layer and a cover.
The golf ball disclosed in Japanese Unexamined Patent Application Publication No. H8-336617 has a soft inner cover, and a hard external cover. This golf ball is spun insufficiently upon shots with a short iron. In addition, this golf ball achieves insufficient flight distance upon shots with a driver.
The golf ball disclosed in US 2002/119840 has a hard external cover. This golf ball is spun insufficiently upon shots with a short iron.
The golf ball disclosed in US 2005/075196 has a hard cover. This golf ball is spun insufficiently upon shots with a short iron.
Requirements for golf balls by golf players have been increasingly escalated. An object of the present invention is to provide a golf ball that is excellent in the flight performance and the control performance.